1. Field of the Invention
The present invention relates to a video signal processing device, and more particularly, to a device for processing a video signal which is to be sub-sampled or which has been sub-sampled.
2. Description of the Related Art
Sub-Nyquist sampling or offset sub-sampling has been attracting attention as a sampling method which achieves compression of a video signal. The principle of such sub-sampling methods will be described below briefly.
During modulation, a luminance signal sampled at, for example, 4 fsc (fsc indicates the color sub-carrier frequency) and a color difference signal sampled at 2 fsc are passed through two-dimensional filters (pre-filters) exhibiting the cut-off characteristics shown in FIGS. 1(a) and 1 (b) , respectively, to remove the component in an oblique direction which does not visually stand out. Thereafter, pixels represented by each of the signals are thinned out alternately on each line, as shown in FIG. 2, to compress the amount of data to one half without generating aliasing noise.
During demodulation, oversampling is performed by inserting `0` for each of the pixels eliminated by the thinning-out process, and then the signals are passed through two-dimensional filters (post-filters) having similar cut-off characteristics to those shown in FIGS. 1 (a) and 1 (b) , to suppress the filter component.
It is thus possible to compress and enlarge image data without greatly deteriorating the image quality.
In such a sub-sampling method, the quality of the demodulated image depends on the cut-off characteristics of the pre-filter and of the post-filter, and the circuit scale depends on the number of taps or coefficients of these filters. In the conventional techniques, the aforementioned pre-filter and post-filter are too large in size and too expensive because of the production cost to be incorporated in household electric appliances.